The present invention relates generally to the field of disc drive storage systems. More particularly, the present invention relates to a pattern zero verification test for a disc drive storage system.
Disc drives are the primary devices employed for mass storage of computer programs and data used in computer systems on magnetic discs. The reliability of the disc drive is, therefore, critical to the operation of the computer systems. As a result, disc drives typically undergo a certification process prior to their shipment to customers. The certification process generally includes a series of tests that are conducted to optimize the performance of the disc drive and ensure that the disc drive meets predetermined specifications. Two such tests are the error rate performance test and the pattern zero verification (PZV) test.
The error rate performance test generally includes multiple writes and reads to data sectors on the disc drive. These multiple writes/reads are used to identify errors on the disc surfaces which indicate that certain sectors on the disc cannot be reliably written to or read from. These errors may arise from defects in the disc media, the disc heads, disc servo mechanisms, noise or other sources. While it is preferable that a disc have no errors associated with it, as a practical matter, disc drives often have various errors, such as media errors, due to manufacturing processes, handling or other causes.
Recognizing this, disc drive manufacturers have established various acceptable error rates for disc drives. Error rates are a measure of the ability to consistently read data from and write data to the disc. The acceptable error rates may be expressed as total numbers of errors for a given number of bytes, maximum acceptable errors of any type of error, or the total number of errors occurring for a given number of bytes read.
Some errors that are encountered can be compensated for using various techniques. One such technique is implemented during the transmission of data and utilizes error correction code (ECC) circuitry along with various ECC formats to perform compensation, which are known in the art. The performance error test is typically implemented in hardware without the need for firmware intervention allowing data detection and correction on-the-fly as the data stream is being read, with the computer system not even being aware that an error was detected.
The PZV test is typically the last test that is performed on the disc drive prior to shipment to the customer. The purpose of the PZV test is to verify that the user data tracks of the discs contain only data bytes representing the value zero. These zero data bytes must be written to the user data tracks, generally during the error rate performance test, in order for some types of software to operate properly. When user data bytes representing a non-zero value (non-zero data bytes) are detected the location of the non-zero data bytes are determined and stored in an error log of the disc drive.
Prior art PZV tests are generally implemented in software and only check the first few hundred tracks, out of the hundreds of thousands of data tracks on a disc. The selected tracks are typically located at the outer diameter of the disc. Accordingly, the percentage of total tracks tested is extremely small. This is primarily due to the fact that the test is very time consuming. For example, the time required to complete the test for 100 tracks is approximately 6 minutes for each disc surface on which data is stored. As a result, the test takes approximately 28 minutes to complete when testing a four head disc drive. Moreover, to scan the entire disc surface of each disc in one four head disc drive, the PZV test would take approximately 79 hours to complete. Consequently, it can be understood why only a small number of data tracks are tested. However, by leaving several hundred thousand tracks of the disc drive untested, there remains a strong potential that some of the data tracks contain non-zero data bytes.
Ideally, the PZV test should be conducted on each of the hundreds of thousands of data tracks of the disc drive to ensure disc drive reliability. Furthermore, the PZV test should be efficient to minimize the duration of the certification process for the disc drive and reduce manufacturing costs. Accordingly, there exists a need for an improved PZV test having greater efficiency than those of the prior art while providing a more thorough analysis of the disc drive.
The present invention is directed to an improved pattern zero verification test having greater efficiency than those of the prior art while providing full disc scan capability. In the method, a data track of the disc drive is read. During the reading of the data track, on-the-fly counting of potential non-zero data bytes (potential count), sectors on which ECC correction has been performed (corrected sector count), and user data bytes on which ECC correction has been performed (corrected byte count) is performed. Next, various conditions of the potential, corrected sector, and corrected byte counts are checked to determine whether the data track includes only zero data bytes.